KR20100106374A - Particle beam assisted modification of thin film materials - Google Patents

Abstract

Several examples of substrate processing methods are disclosed. In a particular embodiment, the method comprises forming a plurality of agents to form at least one crystal in the first region having a grain boundary, without forming another crystal in the second region adjacent to the first region. Introducing 1 particles into a first region of the substrate; And after the introduction of the plurality of first particles is stopped, extending the grain boundaries of the at least one crystal formed in the first region to the second region.

Description

Particle Beam Assisted Deformation of Thin Film Materials

The present application discloses pending US patent application Ser. No. 12/269327, filed Nov. 12, 2008 entitled "Particle Beam Assisted Modification of Thin Film Materials," and "Particle Beam Assisted Modification of Thin Film Materials." Associated with pending US patent application Ser. No. 12/269276, filed Nov. 12, 2008 entitled " Particle Beam Assisted Modification of Thin Film Materials. &Quot; Each pending application is incorporated herein in its entirety by reference.

The present invention relates to systems and techniques for processing a substrate, and more particularly to systems and techniques for forming a substrate crystalline phase.

The widespread adoption of new technologies, such as flat panel displays (FPDs) and solar cells, depends on the ability to manufacture electrical components on low cost substrates. In manufacturing FPDs, the pixels of a typical low cost flat panel display (FPD) are switched by thin film transistors (TFTs), which are made of amorphous silicon deposited on inert glass substrates. Typically made over thin films (-50 nm thick). However, improved FPDs require better pixel TFTs, and it may be beneficial to fabricate high performance control electronics directly on the panel. One advantage may be to eliminate the need for expensive and potentially unreliable connections between the panel and external control circuitry.

Current FPDs are subjected to low temperature deposition processes such as sputtering, evaporation, plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD). Through a layer of Si deposited over the glass panel of the display. Such low temperature processes are preferred because the panels used to make FPDs tend to be amorphous and have a glass transition temperature of approximately 600 ° C. If manufactured at 600 ° C. or higher, the panel may have a non-uniform or uneven structure or surface. There are high temperature resistant glass panels such as quartz or sapphire panels, but the high cost of these glasses makes their use difficult. If lower cost low temperature resistant glass or plastic panels could be used, further cost reduction would be possible.

However, low temperature deposition processes do not produce optimal Si films. As is known in the art, solid Si has three common phases, amorphous, poly-crystalline and mono-crystalline phases. If Si is deposited at low temperatures, the deposited Si film tends to be in an amorphous phase. Channels of thin film transistors based on an amorphous Si film may have lower mobility than those on either polycrystalline Si or monocrystalline Si films.

In order to obtain a polycrystalline or monocrystalline Si layer, the panel can be subjected to additional processes for converting the amorphous Si film into either a polycrystalline or monocrystalline film. In order to obtain a panel having a polycrystalline Si film, the panel may be subjected to an excimer laser annealing (ELA) process. An example of an ELA process can be found in more detail in US Pat. No. 5,766,989. In order to obtain a panel with larger crystals, the panel can go through a process known as a sequential lateral solidification (SLS) process. An example of an SLS process can be found in US Pat. No. 6,322,625. Panels with monocrystalline or polycrystalline Si thin films can be obtained by ELA and SLS processes, but each process is not without drawbacks. For example, excimer lasers used in both processes can be expensive to operate and can be expensive TFTs. In addition, the duty cycle may not be optimal for the best conversion of amorphous Si to crystalline Si. In addition, the excimer laser may have pulse-to-pulse variations that may affect the uniformity of the processes and spatial non-uniformity in the delivered power. For example, there may be intra-pulse non-uniformity that may be caused by self-interference of the beam. By such inter-pulse and intra-pulse nonuniformity, Si films having non-uniform crystals can be obtained.

As such, there is a need for new methods and apparatus for particle processing for producing high quality crystalline materials on low temperature substrates that are cost effective and productive.

An object of the present invention is to provide a substrate processing method for forming a substrate crystal phase.

Several examples of substrate processing methods are disclosed. In a particular embodiment, the method comprises forming a plurality of agents to form at least one crystal in the first region having a grain boundary, without forming another crystal in the second region adjacent to the first region. Introducing 1 particles into a first region of the substrate; And after the introduction of the plurality of first particles is stopped, extending the grain boundaries of the at least one crystal formed in the first region to the second region.

The invention will be described in more detail with reference to exemplary embodiments as shown in the accompanying drawings. Although the present invention is described below with reference to exemplary embodiments, it should be understood that the present invention is not limited thereto. Those skilled in the art, having access to the teachings herein, are within the scope of the present invention as described herein and other embodiments, modifications and embodiments as well as other embodiments in which the present invention may be of significant utility may be used. You will recognize the field of use.

According to the present invention, it is possible to produce high quality crystalline materials on low temperature substrates which are cost effective and productive.

BRIEF DESCRIPTION OF DRAWINGS To help a more complete understanding of the present invention, reference is made to the accompanying drawings, in which like features are referred to by like numerals. These drawings are not intended to limit the invention, but merely to illustrate.
1 is a block diagram of various mechanisms that allow an amorphous material to be converted to a crystalline material.
2 shows a graph of the depth of argon ions introduced to a Si substrate in accordance with an embodiment of the present invention.
3 shows a block diagram of a system for processing a substrate in accordance with an embodiment of the present invention.
4 illustrates a block diagram of a particular example system for the system shown in FIG. 3.
5 shows a block diagram of another system for processing a substrate according to another embodiment of the present invention.
FIG. 6 shows a graph comparing the temperature of a substrate irradiated with a laser beam or particle beam.
7 shows a graph of the temperature of a substrate irradiated with focused particle beams in accordance with another embodiment of the present invention.
8A-8B illustrate a method that may be included in solar cell fabrication in accordance with another embodiment of the present invention.
9A-9C illustrate another method that may be included in solar cell fabrication in accordance with another embodiment of the present invention.
10A-10D illustrate another method that may be included in solar cell fabrication in accordance with another embodiment of the present invention.

In order to overcome the above and other drawbacks to the treatment of existing laser-based thin film materials, several embodiments of particle based processing are disclosed. Particle-based treatment can be beneficial because particle-based treatment can promote non-equilibrium processes. In addition, the particle parameters can be controlled much more accurately than the parameters of the laser. Examples of particle parameters include spatial parameters (such as beam size and current densities), particle flux (and / or beam current), particle species, particle dose, and the like. It may include.

In the present invention, various embodiments are directed to a beamline ion implantation system and a plasma based substrate processing system such as, for example, a plasma assisted doping (PLAD) system or a plasma immersion ion implantation (PIII) system. Is disclosed in connection with. However, those skilled in the art should appreciate that the present invention is equally applicable to other systems, including other types of particle based systems. The term 'particles' as used herein may refer to sub-atomic, atomic or molecular particles that are charged or neutral. For example, the particles may be protons; Ions, atoms or molecules; Or gas clusters.

In the present invention, several embodiments are disclosed in connection with a substrate. The substrate may be a wafer (eg, Si wafer) or may be a substrate including a plurality of films. In addition, the substrate may comprise an element substrate (eg, Si wafer or metal foil) comprising only one element; Compound substrates containing two or more elements (e.g., SiGe, SiC, InTe, GaAs, InP, GaInAs, GaInP; CdTe; CdS; and CuInGaSe, CuInSe2, , Ga, and / or In) and combinations with (S, Se and / or Te), ie other Group III-V semiconductors and other Group II-VI compounds); And / or alloy substrates. Materials contained in the substrate may be metals, semiconductors, and / or insulators (eg, glass, polyethylene terephthalate (PET), sapphire and quartz). The substrate may also be a thin film substrate (eg, SOI) containing multiple layers. If the substrate comprises multiple layers, at least one of the layers may be a semiconducting film or a metal film, while the other of the films may be an insulator. The semiconductive or metal film may be disposed over a single insulating film, or alternatively, may be sandwiched between a plurality of insulating films. In contrast, the insulating film may be disposed on a single semiconducting or metal film, or alternatively, may be sandwiched between multiple semiconducting or metal films or both.

Phase transformation

The fastest mechanism for the crystallization of thin amorphous layers is solid phase epitaxial re-growth (SPER). In SPER, amorphous Si can be converted to crystalline Si by extending the underlying, underlying, pre-existing, extensive crystal layer. This approach is often encountered during annealing to the surface layer of the crystalline Si wafer after the wafer has been amorphous by ion implantation. The present invention relates to the treatment of amorphous substrates in which there is no widespread existing lattice and phase transformation occurs through crystal nucleation prior to the growth of the crystals. Referring to FIG. 1, a block diagram of various mechanisms is shown that allows a material without a wide range of existing lattice to convert from an amorphous phase to a crystalline phase. As is known in the art, crystalline phases may be classified as either polycrystalline or monocrystalline phases. Polycrystalline phases can often be further subdivided into different categories (such as multi, micro, nano crystalline, etc.) depending on the crystal size. However, this distinction may not be important in connection with the present invention and may not be necessary to explain FIG. 1. Thus, these phases may be referred to collectively as crystalline phases herein.

As shown in FIG. 1, phase transformation from an amorphous phase to a crystalline phase can occur through various mechanisms. For example, the conversion may occur through a melting and solidification mechanism 100a and a solid phase crystallization (SPC) conversion mechanism 100b. In the melting and coagulation mechanism 100a and the SPC mechanism, transformation can occur through nucleation of crystallites and growth of sperm. In the SPER mechanism, the transformation can be caused by growth over a wide range of existing crystal lattice.

In the melting and solidification mechanism 100a, energy in the form of radiation, heat, or kinetic energy may be introduced to a portion of the amorphous substrate to melt that portion. If the state of the molten region is suitable for inducing nucleation (eg, supercooling), the crystals can perform nucleation as explained by traditional nucleation theory. Crystals can be nucleated in two ways. Crystals can be heterogeneously nucleated on existing seeds. Existing seeds may be grain boundaries of existing crystals that did not melt upon introduction of energy. Existing seeds may be the boundary between the molten region and the adjacent solid region. If there are no existing seeds, the crystals can homogeneously nucleate. In nucleation, crystals can grow until growth stops.

In solid phase transformation mechanism 100b, phase transformation can occur despite the absence of melting. For example, crystals can nucleate in the region where energy is introduced, followed by growth of nucleated crystals after nucleation. As in the melting process, nucleation during SPC can occur heterogeneously in the presence of existing seeds and homogeneous in the absence of such seeds.

Particle Assist Processes

In the present invention, particles can be introduced to a substrate to induce phase transformation. The phase change may be a phase change from an amorphous phase to one of a polycrystalline and / or single crystal phase. Phase transformation can also occur through nucleation and growth of crystals. To induce conversion, particles may be introduced near the top of the substrate, the bottom of the substrate, or the region between the top and bottom, or a combination thereof. If the substrate comprises two or more different materials, particles may be introduced in the region near the interface of the different materials.

Particle species

Multiple types of particles can be introduced to induce phase transformation. For example, particles that are chemically and / or electrically inert to the substrate can be used. However, chemically and / or electrically active materials may be used. As mentioned above, the particles may be charged or neutral subatomic particles, atomic particles, or molecular particles, or a combination thereof. In some embodiments, molecular particles are preferred. In other embodiments, cluster particles are preferred. Molecular and cluster particles may be preferred because they can be introduced to the substrate at much higher doses and energies. In particular, the molecules and cluster particles introduced to the substrate may disintegrate upon impact, and the kinetic energy of the particles may be divided by the ratio of atomic masses of the particle atoms. Overlapping collision cascades can achieve results similar to the introduction of atomic particles at much higher dose rates. Due to their larger mass, molecular particles may be introduced to the substrate at much higher energy. The generation of atomic and molecular species at the injector, PLAD and PIII will be familiar to those skilled in the art. A detailed description of the generation of cluster particles can be found in US Pat. No. 5,459,326, which is incorporated by reference in its entirety.

The choice of particles introduced into the substrate may depend on the effects of the particles on the substrate. Some features and illustrative examples are shown in Table 1.

Characteristic Exemplary Species Electrically inactive in silicone Ge, Si, C, F, NH, He, Sn, Pb, hydrocarbon molecules, molecules containing C and two or more other elements, hybrids of silicon such as tetra-silane ( hydrides), Si and molecules containing two or more other elements Dopants B, P, As, Sb, In, Ga, Sb, Bi, Shallow Junction Co-Injection Species C, F Amorphous Noble gases (including He, Xe), Ge, Si Strain generation Ge, C Bandgap Fabrication Yb, Ti, Hf, Zr, Pd, Pt, Al Passivating H, D Combined Pinning N Crystallization catalysts Ni, metals

Table 1-Some possible choices of ionic species

Depth and energy

When the particles are introduced to the substrate, the kinetic energy of the particles can be transferred to the substrate. The magnitude of the kinetic energy delivered can vary depending on the size, mass and energy of the particles. For example, heavy ions introduced to a substrate may experience more nuclear stopping than light ions. When particles lose their kinetic energy through a nucleation stop mechanism, this mechanism creates defects such as dangling bonds, vacancies and di-vacancies, for example. There is a tendency, and the presence of such defects can improve the crystallization process. At the same time, the kinetic energy transferred to the substrate through the electron stop can cause crystallization.

Depending on the energy of the particles, the location of the particles delivery, and the properties of the substrate (eg, the thermal conductivity, heat capacity, and melting temperature of the substrate), nucleation of the crystals may be at the top of the substrate; Bottom surface of the substrate; An area between the top and bottom surfaces; Or in the vicinity of the interface of different materials. Thereafter, the phase transformation can continue in the direction away from the position where the transformation is started.

Unlike radiation based phase transformation, the energy deposited on the substrate through particle introduction can form peaks at the surface or, alternatively, below the surface. In addition, the particles can be introduced into the substrate in a constant energy state. Alternatively, particles can be introduced into varying energy states. For example, the energy of the particles introduced into the substrate can change while the particles are introduced. Changes in energy can occur continuously or sequentially. If a beamline particle system is used, the particle energy may be altered during particle introduction using acceleration or deceleration voltages associated with the beamline systems described herein. If PLAD, PIII or other plasma based systems are used, the energy can be changed during the introduction by changing the voltage applied to the substrate.

2, there is a graph showing the depth and energy of particles introduced into a substrate according to an embodiment of the present invention. In this embodiment, argon ions are implanted into the Si thin film. As shown in FIG. 2, the points associated with the lines represent the average range of argon ions, and the vertical error bars represent the straggle in depth. Thus, the total range of all ions can be estimated by the sum of the average range plus a plurality (one or more) of strangles. If argon ions are required to be included in the surface layer of Si of known depth, the maximum energy can be estimated from this curve. The inset chart is an expanded representation of the low energy range of the main chart.

Spatial and Temporal Profiles

In addition to energy, the spatial and temporal profiles of the particles can be controlled. For example, the particles can be introduced as a particle beam, and the beam can have a constant or varying beam current density (ie, the number of particles in a preset region over a preset time). Current density may be particle current and / or beam size; Beam dwell time by control of beam and / or substrate scan rates and / or pulse length; And beam duty cycle (eg, the time between beam pulses or the return time when the beam and / or substrate is scanned).

In the present invention, the particles can be introduced into the substrate either continuously or periodically in sequence. If the particles are introduced as a particle beam, the beam can have various forms. For example, the particles can be introduced as a ribbon beam or spot beam. The ribbon beam may have a ribbon shape or a shape in which the beam dimension along one direction is larger than along the other direction. Such ribbon beams may be wider than the substrate or, alternatively, narrower than the substrate. On the other hand, the spot beam may have a smaller dimension than the substrate. If a spot beam is used, the spot beam can be scanned magnetically or electrostatically at a rate of approximately 100-1000 Hz to resemble a ribbon beam.

If the cross section of the beam is smaller and does not cover the entire surface area of the substrate, whether it is a ribbon beam or a spot beam, the beam can be scanned further against the substrate. For example, the beam can be scanned along two directions, ie, in the width direction and in the length direction, so that particles can be introduced to the entire surface of the substrate. In the present invention, such a scan can be accomplished by translating the substrate along the length and width directions with respect to the fixed beam, or by translating the beam along the length and width directions with respect to the fixed substrate. By controlling the rate of relative scan of the beam and / or substrate, the phase change of the substrate can be controlled.

In addition, the particle beam introduced into the substrate may be a focusing beam or a non-focused beam. In addition, the beam of particles may be uniform or nonuniform along its cross section. For example, the ribbon beam may have a higher current density at its leading edge that precedes the trailing edge with a lower current density, and vice versa. The non-uniform beam may have different intensity profiles. It is believed that heterogeneous beams can improve nucleation and growth processes. For example, a non-uniform beam may have a strong leading edge and a less strong trailing edge along it to initiate nucleation. For example, the high density portion of the beam can initiate phase transformation by melting the substrate, and the low density portion of the beam can improve the scale of the transformation by controlling the solidification of the molten region.

In addition, two or more beams may be activated and introduced into the substrate simultaneously or sequentially. If two or more beams are used, the beams may be introduced into the entire width and / or length of the substrate at one time.

direction

Particle assisted phase transformation may have several advantages in crystal growth and / or orientation of the crystal form. In the present invention, the particles can be introduced to the substrate at various angles. Introducing particles at various angles may be accomplished by tilting the substrate with respect to the beam, and / or the beam may be tilted with respect to the substrate.

In one embodiment, particles may be introduced to the substrate at 0 ° (ie, perpendicular to the surface of the substrate). Particles introduced at 0 ° may preferentially destroy {200} grain boundaries, which may limit electrical conductivity in FPDs. Alternatively, the particles can be introduced at different angles, for example 7 °.

Board Status

In addition to the parameters of the particles, the states of the substrate can be adjusted before, during or after the introduction of the particles. For example, the temperature of the substrate can be adjusted. In one embodiment, the substrate may be heated to, for example, approximately 500 ° C. before or during the introduction of the particles. Heating the substrate can mitigate thermal shock caused by the particle beam. In addition, heating the substrate may lead to the formation of larger crystals. For example, heating the substrate can cause the region into which the particles are introduced to cool at a slower rate (since this region loses most of its energy through the conduction).

If the substrate is cooled below room temperature, crystallization can be improved. For example, the substrate can be cooled to a temperature in the range of about 0 ° C to about -100 ° C. In addition, cooling the substrate can prevent the insulating film structure from becoming unstable.

When the particles are introduced to the substrate, the substrate may be in vacuum or at atmospheric pressure. Vacuum pressure may be higher than that normally associated with ion implantation (ie, pressures higher than 10-4 mbar) to reduce pump costs.

Example Systems

Referring to FIG. 3, a block diagram of an example system 300 for processing a substrate in accordance with an embodiment of the present invention is shown. System 300 may be beamline particle system 300. System 300 includes an ion source 302; Extraction system 304; Acceleration system 306; Optional beam manipulation components 308; And a neutralization system 310. The system 300 may also include an end station 312 in communication with the neutralization system 310. Termination station 312 may include a window 314 and one or more loadlocks 316 and 318. Inside the termination station 312, a platen supporting the substrate 322 may be located. In addition, one or more substrate translation, cooling and / or heating sub-systems 324 may be disposed in the end station 312.

In the present invention, the ion source 302 may be a Bernas type having an indirect heating cathode. Those skilled in the art will appreciate that the ion source 302 may be other types of ion sources. On the other hand, extraction system 304 may be a single slit or, alternatively, multiple slit extraction system 304. Extraction system 304 may be translatable in one or more orthogonal directions. In addition, extraction system 304 may be designed to extract a constant beam current in time. In addition, extraction system 304 can extract particles continuously or intermittently. Extraction system 304 may focus the particle beam or beamlets to enable desirable spatial and / or temporal beam profiles. The beam of particles extracted through the extraction system 304 may have an energy of approximately 80 keV.

If higher energy is needed, the system 300 can include an acceleration system 306 that can accelerate the particle beam. System 300 may include one or more additional and optional beam manipulation components 308 for filtering, scanning, and shaping particles into the particle beam. As shown in FIG. 4, a particular example of system 300, that is, optional beam manipulation components 308 may include a first magnet analyzer 406, a first deceleration (D1) stage 408, A second magnet analyzer 410, and a second deceleration and a second deceleration (D2) stage 412. In the present invention, the first magnet analyzer 406, which is substantially a dipole magnet, is based on the mass and energy of the particles so that particles of unwanted mass and / or energy do not pass through the magnet analyzer 406. The particles can be filtered. On the other hand, the second magnet analyzer 410, which is substantially another dipole magnet, may be designed to collimate the particles into a particle beam having a desired shape (eg, ribbon) and / or dimensions. The D1 and D2 deceleration stages 410, 412 can manipulate the energy of the passing particles so that the particles can be introduced into the substrate in the desired energy state. In one embodiment, D1 and / or D2 may be segmented lenses capable of minimizing the space charge effect and maintaining the spatial integrity of the beam.

Although not shown, the beam manipulation components may include one or more substantially quadrupole lenses or einzel lenses for focusing the beam. In addition, the beam manipulation components may include magnetic multipoles or rods as described in US Pat. Nos. 6,933,507 and 5,350,926 to control the uniformity of the beam profile.

Returning to FIG. 3, in accordance with this embodiment, a charge neutralization system 310 may be included to reduce build-up at the substrate 322. The charge neutralization system 310 may be one or more systems of hot filament, microwave, or rf driven as described in US patent application Ser. No. 11/376850. Alternatively, the charge neutralization system 310 may be an electron source.

At the end station, the environment surrounding the substrate can be controlled, for example, to prevent deposition of other materials on the substrate or to facilitate passivation to enhance the crystallization process. In order to control the environment, the termination station 312 includes a thin foil window or differentially pumped opening 314 through which particles may enter and one or more load locks 316 and 318 into which the substrate may enter. ) May be included. The load locks 316, 318 may be replaced with one or more differential pumped stages on which the substrate may enter.

Termination station 312 may include substrate movement, cooling, and heating subsystem 324. Examples of subsystem 324 may include a chiller, a heat source, and a roplat that can translate / rotate the substrate along several axes. Specific examples of chillers can be found in US patent applications 11 / 504,367, 11 / 525,878 and 11 / 733,445, each of which is incorporated herein by reference in its entirety. Specific examples of heat sources may be lasers, flash lamps, platens providing fluid heating, resistive heat sources, or those described in US patent applications Ser. Nos. 11 / 770,220 and 11 / 778,335, respectively. Patent applications are incorporated herein in their entirety by reference.

In order to monitor process and substrate parameters / states, one or more parameters / states measuring components may be included near the substrate 322. Such components can be coupled to one or more controllers, which can control the parameters / states and / or particles of the substrate based on signals from the measurement components.

5, another exemplary system for processing a substrate according to another embodiment of the present invention is shown. In particular, system 500 may be a PLAD, PIII system, or other plasma based substrate processing system. The PLAD system 500 may include a chamber 501 that includes a top section 502 and a bottom section 504. The upper section 502 may include a first dielectric section 506 generally extending in the horizontal direction and a second dielectric section 508 extending generally in the vertical direction. In one embodiment, each dielectric section 506, 508 may be a ceramic that is chemically resistant and has good thermal properties. The upper section 502 may include at least one antenna 510, 512. One or more antennas 510, 512 may be, for example, horizontal antenna 510 and / or vertical antenna 512. In one embodiment, the horizontal antenna 510 may be a planar coil with multiple windings, while the vertical antenna 512 may be a spiral coil of multiple windings. At least one of the antennas 510, 512 may be electrically coupled to the power supply 514 via an impedance matching network 516.

Above the lower section 504 of the system 500, the platen 520 and the substrate 522 supported by the platen 520 may be located at a predetermined height below the upper section 502. However, it is also contemplated that platen 502 and substrate 522 may be located in upper section 502. The bias voltage power supply 524 may be electrically coupled to the platen 520 to apply a DC or RF bias to the platen 520.

In operation, at least one of the antennas 510, 512 may be supplied with RF or DC power by the power source 514. If only one of the antennas 510, 512 is supplied with RF or DC power, the other of the antennas 510, 512 may be a parasitic antenna. Since the other of the antennas 510, 512 is not electrically coupled to the power source 514, the other of the antennas 510, 512 may be a parasitic antenna. Instead, the other of the antennas 510, 512 is magnetically coupled to the antenna powered by the power source 514. Alternatively, both antennas 510, 512 can be powered by power source 514 with RF current. Next, at least one of the antennas 510, 512 directs RF currents to the system 500 through the first and second dielectric sections 506, 508. Electromagnetic fields induced by RF currents may convert the gas contained in the system 500 into a plasma. On the other hand, the bias voltage power supply 524 biases the platen 520 to attract the charged particles in the plasma state to the substrate 522. Further details of system 500 may be found in US patent application Ser. No. 11/766984; US Patent Application Publication No. 2005/0205211; US Patent Application Publication No. 2005/0205212 and US Patent Application Publication No. 2007/0170867, each of which is incorporated herein by reference in its entirety.

Optional parts

In addition to the components described above, example systems 300-500 may optionally include one or more masks between a particle source (eg, an ion source or plasma) and a substrate. If such a mask is included, the mask may preferentially be a carbon (C) based material, a Si based material (eg SiC), or a refractory metal containing material such as W or Ta. However, other materials may be used. Such a mask may have one or more openings of various shapes, including a chevron shape, to control the shape of the beam incident on the substrate.

FPD

A description of the various applications of particle induced phase inversion is provided below. As described above, particles can be introduced into the Si layer of the thin film substrate to induce phase transformation from the amorphous phase to the crystalline phase. For clarity, particle induced phase inversion is compared with the ELA process.

In this embodiment, the particles can be sent to FPD with an amorphous Si film of about 500 microns thick disposed over the insulating film. The insulating film can be, for example, amorphous glass or Corning 1737 glass, quartz, plastic, or sapphire with a thickness of about 0.7 mm. However, one skilled in the art will recognize that other types of insulating films may be used.

In the ELA process, a single laser pulse can deliver an energy pulse of 360 mJ / cm 2, which is a 12 nanosecond long pulse. This corresponds to a power density of 3 x 10 ¹⁰ W / m ² . If an argon ion beam is directed to the Si film, the beam can have an energy of 20 keV. By this energy, all of the argon ions sent may not penetrate into the substrate beyond the Si layer (see FIG. 2). If a ribbon argon particle beam is used, it can be assumed that the beam has dimensions of 300 mm wide and 0.1 mm long. With a beam current of 25 mA, this suggests a power density of 1.7 x 10 ⁷ W / m ² .

In an ELA process, a laser beam incident on the substrate may heat the Si layer to 1000 ° C., which is near the melting temperature of amorphous Si. Upon incidence, the laser beam may initiate at least partial melting of the Si layer. Thermal diffusivity for Si varies relatively largely between ˜1 cm 2 / sec at room temperature and 0.1 cm 2 / sec at 1400K. For this reason, even if the laser energy is absorbed in the upper few nm of the Si surface, there can be a very small temperature gradient in the Si layer without any latent heat effects. Heat can diffuse from Si into the glass. Since the diffusivity to glass is small (˜0.005 cm 2 / s for large temperature ranges), a large thermal gradient may exist across the thick glass layer. The results of the model shown in FIG. 6 yield that even glass within 0.1 μm of Si does not reach above 500 ° C.

Since the particle beam has a lower power density, the exposure time required to accumulate enough energy to heat the Si film can be high (80 ms) compared to the laser 12 ns. In addition, more energy may be needed to sufficiently heat the Si film because heat accumulated in the substrate through the particles may be lost to insulation through thermal conduction. Under these assumptions, an insulating film within 50 μm of Si may be heated to 600 ° C. or higher. Nevertheless, a sufficient amount of insulating film may not be heated above the glass transition (or melting) temperature such that these conditions are acceptable.

If the height of the ribbon beam is increased to 1 mm, it may take approximately 2.4 seconds to sufficiently heat the Si film, and within this time the peak temperature of the glass bottom can reach 600 ° C. Compared to the 0.1 mm case of FIG. 7, this example shows that the power density of the beam needs to be kept as high as possible. This can be accomplished by keeping the beam area as small as possible, increasing the beam current, and / or increasing the beam energy. The mass of ionic species can also be increased. It may be desirable to use molecular particle beams because molecular particle beams allow the use of higher beam energies. At the same time, higher beam energy can reduce additional deleterious effects such as space charge blow up, and if the beam energy is not higher, space charge explosion can limit beam currents and beam focusing. have.

Particle beam irradiation can keep solid Si in an amorphous phase, causing melting to occur at 1300K. Crystalline Si does not melt to 1683K. Thus, if amorphous Si is crystallized before the start of melting, more power may be needed to fully melt the material. Liquid Si can also reflect a portion of the laser radiation, so once the Si surface is melted, it can be difficult to couple power to the bulk of Si. The presence of the particle beam and the crystallization phase being cooled can affect the production of high quality materials.

Thin film solar cells

The particle induced phase transformation described in the present invention may be applied to the manufacture of thin film solar cells. As is known in the art, amorphous Si is able to absorb light more efficiently than crystalline Si, which is a direct band gap material and an indirect band gap material. In addition, amorphous Si absorbs more light in the visible spectrum than crystalline Si. However, amorphous Si has lower electrical conductivity. As such, amorphous Si can preferably convert incident radiation to current, while crystalline Si can preferably deliver the generated current. Thus, it may be desirable for the solar cell according to this embodiment to have a layer of amorphous Si over another layer of crystalline Si. Incident radiation of visible wavelengths can be efficiently converted from amorphous Si to photocurrent. Unconverted light in the amorphous layer (including infrared radiation) can be converted into photocurrent in crystalline Si.

Referring to FIG. 8, a process that may be included in substrate processing in accordance with another embodiment of the present invention is shown. In this embodiment, the substrate can be a thin film solar cell with crystalline and amorphous layers. In another embodiment, the substrate may be a semiconductive layer of FPD disposed over an insulating layer (not shown). As shown in FIG. 8A, an amorphous Si layer 802 may be deposited over a glass layer (not shown). The Si layer 802 may have a thickness of 1.5 μm, while the glass layer may have a thickness of 3 mm. Next, particles 804 with predetermined dose and energy may be introduced into the amorphous Si layer 802. As shown in FIG. 8B, particles 804 may be introduced below the surface of the Si layer to crystallize the lower portion of the Si layer 802 without inducing crystallization of the upper portion of the amorphous Si layer 802. Can be. The ultimately obtained substrate can be used in a solar cell having an amorphous Si layer 802 disposed over a crystalline Si layer 806.

9, a process that may be included in substrate processing according to another embodiment of the present invention is shown. In this embodiment, the substrate can be a thin film solar cell with crystalline and amorphous layers. In another embodiment, the substrate may be a semiconductive layer of FPD disposed over an insulating layer (not shown). As shown in FIG. 9A, an amorphous Si layer 902 may be deposited over a glass layer (not shown). Thereafter, particles 904 with preset dose and energy may be introduced into the amorphous Si layer 902 to crystallize the entire Si layer 906 (FIG. 9B). As shown in FIG. 9C, a plurality of particles of the second species 908, energy and dose may be introduced into the substrate to amorphous the layer near the surface of the crystalline Si layer. The solar cell ultimately obtained may have an amorphous top Si layer 904 and a bottom crystal Si layer 902.

Referring to FIG. 10, a process that may be included in substrate processing according to another embodiment of the present invention is shown. In this embodiment, the substrate can be a thin film solar cell with crystalline and amorphous layers. In another embodiment, the substrate may be a semiconductive layer of FPD disposed over an insulating layer (not shown). As shown in FIG. 10A, an amorphous Si layer 1002 may be deposited over a glass layer (not shown). Thereafter, particles 1004 having a predetermined dose and energy are introduced into the amorphous Si layer 1002 to crystallize the sub-layer 1006 (see FIG. 10B) in the Si layer 1002. Can be. Although FIG. 10B illustrates a sublayer disposed near the top surface of the Si layer 1002, those skilled in the art may place the sublayer 1006 anywhere near the top surface, near the bottom surface, or anywhere between the top and bottom surfaces of the Si layer 1002. It should be recognized.

After forming crystalline sublayer 1006, one or more crystals of sublayer 1006 may be grown from sublayer 1006 until the entire Si layer 1002 can be crystallized. Crystals can be grown through one of furnace annealing, rapid thermal annealing (RTA), flashlamp annealing and laser annealing. Alternatively, the crystals can be grown by particle assisted annealing. For example, the same or different types of particles with different preset doses and / or other preset energies may be introduced into the region below the crystallized sublayer to extend the grain boundaries of the one or more crystals towards the bottom surface of the substrate. Can be. In the process, the entire Si layer 1002 may include one or more crystals with grain boundaries extending in the vertical direction. This embodiment may include an optional amorphous step to amorphous the portion of the newly crystallized Si layer 1006. For example, particles 1010 may then be introduced into the newly crystallized Si layer 1002 to form at least a portion of the newly crystallized Si layer 1002 (FIG. 10D) to form an amorphous sublayer 1012. Amorphize. In the present invention, the particles introduced to newly crystallize the Si layer 1002 may be the same particles used to crystallize the previous amorphous Si layer 1002. Alternatively, the particles introduced to newly crystallize the Si layer 1002 may be different than those used to crystallize the previous amorphous Si layer 1002. The process can be used to crystallize a thick amorphous Si layer.

Particle induced phase conversion may be used to make efficient polycrystalline Si solar cells. The grain boundaries of the crystals can be places efficient for gettering impurities such as metal contaminants. In addition, the grain boundaries can serve as a barrier to the mobility of charge carriers that prevent carriers from moving through the boundary. Thus, if grain boundaries are disposed across the path of charge carriers, polycrystalline solar cells having a large number of crystals, and consequently a plurality of grain boundaries, may have a relatively low electrical conductivity. In polycrystalline solar cells, the current generated on the top side has to be transferred to a contact region that is generally located on the bottom side of the solar cell. If the grain boundaries of polycrystalline solar cells are located across the path of charge carriers, the efficiency of the solar cells can be lowered. As such, it may be desirable to fabricate polycrystalline solar cells having grain boundaries that are oriented in a parallel manner with respect to the path of charge carriers.

In order to produce an efficient polycrystalline solar cell, an amorphous Si substrate can be prepared. The top surface of the Si layer can then be crystallized and the crystals can grow down for solid phase epitaxial regrowth (SPER). Ion energy can be selected to maximize the power density delivered to the substrate. This may correspond to an energy between 40 and 100 kev, in which case typical ion beam systems can extract maximum beam currents from an ion source, and space charge effects are reduced for beam transport and focusing. This ion beam can cause crystallization near the silicon surface, which can seed the SPER down until the entire layer is crystallized. SPER may occur as part of the beam induced crystallization step, or may occur in a further annealing step that may use one or more of a furnace, RTA, flashlamp, laser or other annealing methods. The ultimately obtained substrate will likely have crystals with grain boundaries extending vertically. Thereafter, particles of the second species, energy and dose can be introduced to the substrate to amorphous the layer near the surface of the polycrystalline substrate. Thus, the solar cell may have a structure of an amorphous Si layer over a polycrystalline Si layer extending vertically. As mentioned above, such solar cells can convert radiant energy into electrical energy more efficiently, and at the same time, transfer the converted electrical energy more efficiently.

In the present invention, the size and orientation of the boundaries can be influenced by the choice of particle beam states used to assist in crystallization of the top layer. Phosphorous may be the preferred species because it is a good getter species and may be the dopant of choice for solar cells. The direction of implantation can be chosen to affect particle orientation. To create an upper crystalline surface with little voids, the entire active layer can be implanted or the surface layer can be implanted and the rest of the substrate can be regrown by SPER.

The terms and expressions employed herein are used in the meaning of description rather than limitation, and in the use of these terms and expressions are not intended to exclude any equivalents of the features (or portions thereof) shown and described. It should be recognized that various modifications are possible within the scope of the claims. Other variations, modifications and alternatives are possible. Accordingly, the foregoing description is for the purpose of illustration only and of limitation. The claims are any feature that is described in detail herein.

302 Ion Source 304 Extraction System
306: acceleration system 308: beam manipulation components
310: charge neutralization system 322: substrate
324: Substrate Translation Heating and Cooling Subsystem

Claims (34)

In order to form at least one crystal having a grain boundary in the first region without forming another crystal in the second region adjacent to the first region, a plurality of first particles are formed in the first region of the substrate. Introducing to; And
After stopping the introduction of the plurality of first particles, extending the grain boundaries of the at least one crystal formed in the first region to the second region. The method according to claim 1,
And the first region is an amorphous phase that is part of the substrate. The method according to claim 1,
Wherein the first region is close to an upper side of the substrate, and extending the grain boundaries to the second region includes extending the grain boundaries toward the lower side of the substrate. . The method according to claim 1,
Wherein the first region is close to a lower side of the substrate, and extending the grain boundaries to the second region includes extending the grain boundaries toward the upper side of the substrate. . The method according to claim 1,
Wherein said region is spaced apart from an upper side and a lower side, and extending said grain boundary to said second region comprises extending said grain boundary toward an upper side and a lower side of said substrate. The method according to claim 1,
And said at least one crystal in said first region is an amorphous phase formed through solid phase nucleation. The method according to claim 1,
Extending the grain boundary to the second region is an amorphous phase that can be achieved through solid phase epitaxial regrowth. The method according to claim 1,
Introducing at least a portion of the first region into at least a portion of the first region to amorphousize at least a portion of the first region. The method according to claim 7,
And wherein the amorphous portion is adjacent to an upper surface of the substrate, the substrate comprises a plurality of crystals, the plurality of crystals being amorphous with grain boundaries extending along a vertical direction. The method according to claim 1,
Extending the grain boundary is an amorphous phase performed by one of furnace annealing, rapid thermal annealing (RTA), flashlamp annealing, and laser annealing. The method according to claim 1,
Extending the grain boundary to the second region is an amorphous phase performed by grain assisted growth. The method of claim 11,
And wherein said particle assisted annealing comprises introducing a plurality of third particles into said second region. The method of claim 12,
Wherein said particle assisted annealing further comprises controlling energy of said third particles. The method according to claim 13,
And adjusting the energy of the third particles comprises increasing the energy of the third particles. The method according to claim 1,
Wherein said substrate is an amorphous phase, said Si layer of an FPD product comprising a Si layer disposed over an insulating layer. The method according to claim 1,
And said substrate is an amorphous phase which is a solar cell panel. The method according to claim 1,
Wherein said first particles are amorphous being introduced into said first region at 5 × 10 ¹⁴ particles / cm ² sec or greater. The method according to claim 1,
And said first particles are amorphous being introduced into said first region as a focusing particle beam. The method according to claim 18,
And wherein said focusing particle beam is amorphous having a cross-sectional density profile that decreases from a first cross-sectional end to a second cross-sectional end. The method according to claim 1,
And the first particles are amorphous containing molecular ions. The method according to claim 1,
And the first particles are amorphous, including cluster particles. The method according to claim 1,
And the first particles are amorphous, including protons or deuterons. The method according to claim 1,
Wherein said first particles are amorphous, comprising at least one species selected from the group consisting of He, Ne, Ar, Kr, Xe and Rn. The method according to claim 1,
And the first particles are Ga in an amorphous phase. The method according to claim 1,
Wherein said first region comprises Si and said first particles are amorphous, comprising at least one species selected from the group consisting of C and Ge, in order to convert said first region into a stressing region. The method according to claim 1,
The first region comprises a material selected from Group IV elements, wherein the first particles are selected from the group consisting of B, Ga, In, P, As, Sb and Bi, in order to alter the electrical properties of the first region. A method of treating a substrate that is amorphous, comprising at least one species selected. The method according to claim 1,
The first region comprises a material selected from Group IV elements, the first particles being a group consisting of Yb, Ti, Zr, Hf, Pd, Pt and Al, in order to change the bandgap characteristics of the first region. A method of treating a substrate that is amorphous in one or more species selected from. The method according to claim 1,
The first region includes a material selected from Group IV elements, and the first particles include C, including particles, Si, including particles, to prevent electrical properties of the first region from changing. An amorphous phase comprising at least one species selected from the group consisting of Ge, F containing particles, N containing particles, H comprising particles, He containing particles, Sn containing particles and Pb containing particles. The processing method of a phosphorus substrate. The method according to claim 1,
Wherein the first region comprises a material selected from Group IV elements, and wherein the first particles are amorphous and include metal particles to increase the rate at which the at least one crystal is formed in the first region. Way. The method of claim 29,
And the metal particles are amorphous containing Ni particles. The method according to claim 1,
And changing the temperature of the substrate prior to introducing the first particles into the first region. 32. The method of claim 31,
Changing the temperature comprises reducing the temperature. The method according to claim 1,
And said first particles are amorphous being introduced into said first region at an angle perpendicular to an upper surface of said substrate. The method according to claim 1,
And the first particles are amorphous and introduced into the first region at an angle other than an angle perpendicular to the top surface of the substrate.

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